QUESTION: Can you explain "Buddha Nature"?
SHORT ANSWER: Buddha nature is no nature.
ANSWER: Buddha nature is no nature. Different writers use the concept in different ways, so to elucidate it one needs to clarify which Buddha nature concept one is referring to. Thus, for instance, there is a common idea that Buddha nature is somehow the core or essence of the person - a kind of soul. This is an idea that has infected Buddhism from time to time, but is not in accord with the principles of non-self, dependent origination and emptiness that are fundamental to the teachings of Shakyamuni. It is more a Hindu or even humanistic psychology idea. A Buddha does not have a fixed nature. A Buddha simply has an absence of malice. However, it has been a problem in the presentation of Buddhism historically that people search for and cling to "positive" forms of expression of the Dharma and this then leads to the coining of many forms of upaya (skilful means). Thus the idea of Buddha nature does not go back to Shakyamuni, but seems to have been invented in the dialectic between Buddhism and other religions. In the West today it is a popular idea because ideas of soul are deeply embedded in Western culture and although people may think they have rejected the theistic ideas, they reinvent them. The soul then becomes the "self-actualising tendency" and so on, and Buddha nature can then be easily saddled onto the same horse. From time to time great teachers - like Nagarjuna - have to come along and dismantle all these constructions. In the meantime, however, if people find them helpful then they are not entirely bad, simply something that will have to be left behind one day.
The idea that there may be something called Buddha nature "within" oneself, therefore, is non-Buddhist. Nagarjuna would no doubt have said that were there any such entity then either it acts or it does not act. If it acts (i.e. if it is the doer of one's "good" deeds, for instance) then it cannot be eternal and must be subject to change, and if it does not act then it has no relevance to life and existence and so is a meaningless idea. Neither way can it really function as one's "true nature". There is no special agent "within" that is responsible for our good and wise actions any more than there is a devil within responsible for our bad and stupid ones. We can loosely and colloquially say that a person is part angel and part devil and so long as we take such expressions lightly and poetically they make sense, but if we try to reify them into a spiritual anatomy of the person we go astray. Buddhism is opposed to that kind of reification in all its varieties.
All this led to a good deal of controversy in Japan in what is called the "critical Buddhism controversy". There is excellent material all about it in the book Pruning the Bodhi Treee by Hubbard & Swanson. There is also a shorter account in my own book The New Buddhism. It is, for instance, sometimes thought that a belief in Buddha nature will make people into better people and insofar as it is simply an expression for seeing the best in others there is much to say for it. However, it has also been pointed out that the deeper logic of the idea that there is an indestructible core of goodness in people leads to the conclusion that it does not matter how badly you treat them because you will never destroy their core anyway, so it does not matter. This idea is strongly developed in the Bhagavad Gita and it is ideas of this kind that Shakyamuni was preaching against. The Critical Buddhists in Japan argue that this line of thinking lies behind many forms of social discrimination in Japanese sectarian Buddhism. We do not need to pursue every detail - sufficient to observe that ideas can be played both ways.
There can also be a kind of subtle arrogance in the idea of thinking that one "has" Buddha nature. It is much safer spiritually to keep one's focus upon one's avidya, upon one's blindness and short-comings. Perhaps I do have a perfect inner nature - so what? Perhaps I have a nature to make mistakes, to hurt people, to be vulnerable - so there is much to do and a basis for fellow-feeling with others. If a person really does have a buddha-ly nature then that person is probably not particularly - if at all - aware of it. It might be noticed by others, but even if the person is told so by such an observer, the person in question is likely to say, "Oh, no, no, I'm just an ordinary foolish being."
Thus, in Pureland, the emphasis is upon our bombu nature. This is the root of compassion, modesty and gratitude. It is also the foundation of faith. If one were already of the nature of Buddha, what need would one have of the help of the Buddhas - one would already have everything one needs. It is only when and as I acknowledge my bombu nature that I open myself to the possibility of being helped, of receiving a grace that may lift me out of my karmic plight.
Paradoxically, when I make such an act of humble faith, I do immediately participate in a certain way in the freedom and emptiness of the Tathagatas, since doing so involves letting go of all that I previously had clung to as my nature, and that is how Buddhas are - having no fixed nature, just willing to be whatever is needed, gratefully receiving whatever comes along.
Another slight, yet relevant, tangent to this line of thought is the question of awareness. As just pointed out, the buddha-ly person is not aware of being buddha-like. Saints are generally humble people more conscious of their sins than their virtues. The common idea that spiritual awakening is a function of becoming aware of one's Buddha nature is, therefore, well wide of the mark. To have a buddha-ly nature means to be somebody who acts in the manner of a Buddha quite naturally and when we do things quite naturally we are not especially aware of them. A Buddha is not acutely aware - a Buddha is a natural. Thus Dogen, in Genjokoan, says that enlightened people are not necessarily aware of being so. Certainly, Buddha nature is not a kind of awareness.